Fluorescent Molecular Sensors Research Articles

Emerging fluorescence sensing technologies: from photophysical principles to cellular applications.

Fluorescent molecular sensors are poised to solve problems in many disciplines. This report outlines their design basis and their applications in the fields of gene expression and neuronal activity. After a long induction period, fluorescent molecular sensors are showing several signs of wide-ranging development (1, 2). The clarification of the underlying photophysics, the discovery of several biocompatible systems, and the demonstration of their usefulness in cellular environments are some of these signs. Another sign is that the beneficiaries of the field are multiplying. They run from medical diagnostics through physiological imaging, biochemical investigations, environmental monitoring, and chemical analysis to aeronautical engineering. The design of fluorescent molecular sensors for chemical species combines a receptor and a fluorophore for a “catch-and-tell” operation. The receptor module engages exclusively in transactions of chemical species. On the other hand, the fluorophore is concerned solely with photon emission and absorption. Molecular light emission is particularly appealing for sensing purposes owing to its near-ultimate detectability, “off/on” switchability, and very high spatiotemporal resolution including video imaging. The commonest approaches to combining fluorophore and receptor modules involve integrated or spaced components (3). The integrated or intrinsic sensor format relies on internal charge transfer within the excited state. The partial electronic charges so separated can interact with the target species when it is trapped by the receptor. The energy of the excited state is thereby disturbed and shows up as a blue- or red-shifted light absorption and/or emission. Roger Tsien’s intracellular Ca2+ sensor fura-2 (Fig. 1) is a …

Peer Reviewed: Fluorescent Molecular Sensor for Drug Discovery.

The tyranny of large numbers of drug compounds to screen is the raison d'être for a fluorescent assay system.

The Molecular Design of Fluorescent Sensors for Ionic Analytes

Molecular fluorescent sensors can be synthesized by covalently linking a photoactive fragment (e.g., anthracene) to a receptor subunit displaying affinity toward the envisaged substrate. The electron transfer process is the privileged signal transduction mechanism: redox active substrates (e.g., transition metals) typically release/uptake an electron to/from the proximate photoexcited fluorophore, the recognition being signaled through fluorescence quenching; redox inactive substrates (d0 and d10 metals, H+) deactivate an existing quenching relay (e.g., a tertiary nitrogen atom close to the fluorophore) and their recognition is signaled through fluorescence enhancement. An-ionic substrates can be conveniently recognized on the basis of the metal–ligand interaction: polyamine receptors containing the photophysically inactive ZnIIion bind the carboxylate group. In the case of amino acids,\({\text{NH}}_3^ + {\text{ - CH(R) - COO}}^ -\), selectivity is improved when the receptor platform bears additional groups capable to interact specifically with the R substituent. If R is capable of transferring an electron to the nearby photoexcited fluorophore, the recognition is signaled through fluorescence quenching.

Fluorescent sensing of uronic acids based on a cooperative action of boronic acid and metal chelate

A new fluorescent molecular sensor for uronic acids is designed, which features two-point interactions of boronic acid–diol complexation and zinc(II)–carboxylate coordination.

Luminescence and charge transfer. Part 2. Aminomethyl anthracene derivatives as fluorescent PET (photoinduced electron transfer) sensors for protons

The importance of the modular structure ‘fluor-spacer-amine ’is pointed out for the design of fluorescent molecular sensors for pH according to the principle of photoinduced electron transfer (PET). Anthracen-9-yl methylamines (24) and some azacrown ether analogues (15 and 23) are examined in this context. They show pH-dependent fluorescence quantum yields describable by eqn. (5) while all other electronic spectral parameters remain essentially pH-invariant. The range of pKa values of these sensors are understandable in terms of macrocyclic effects and the transmission of electric fields across the anthracene short axis. Phase-shift fluorometric determination of the fluorescence lifetimes of these sensors allows the calculation of the rate constant of PET in their proton-free form to be 1010–1011 s–1, with the diamines 23 and 24b exhibiting the faster rates.

Photo-induced electron transfer as a general design logic for fluorescent molecular sensors for cations

The reasons for the value of molecular fluorescence as a biosensing technique are outlined. The case of fluorescent sensors for cations is discussed with emphasis on a new general design logic employing the principle of photo-induced electron transfer.